The most commonly used technique for screening for, and evaluating, breast cancer is the x-ray mammogram. Mammograms are known to be quite uncomfortable for the patient, because the breast is typically compressed during mammographic imaging. Mammograms also expose patients to ionizing radiation, and contrast between tumor and non-tumor tissue, including inhomogenicities due to fibrocystic disease, is often lacking.
Alternatives to mammograms, both for screening and for noninvasively evaluating potentially malignant tissue, have been sought. These alternatives include various forms of near-infrared diffuse tomographic imaging, as well as microwave imaging.
Microwave imaging has advantage over conventional mammography because it does not involve sometimes painful compression of the breast, does not involve ionizing radiation, and system cost may be lower than for competing technologies, including MRI-based imaging.
There is a subset of the population with dense breasts. Dense breast tissue is difficult to distinguish from tumor both with mammography and microwave imaging because, in such breasts, the endogenous contrast between tumor and the naturally occurring fibroglandular and fibrocystic tissue, is not as high as it is in fattier breast tissue.
It is expected that improving the contrast between tumors and all normal breast tissue—not just the adipose tissue—will have a significant impact on improving microwave imaging detection and characterization capability. Along this line, the University of Wisconsin microwave imaging team has been working towards developing viable dielectric property contrast agents, including microbubbles and single walled carbon nanotubes (SWCNT) [Mashal et al 2009, 2010]. Both of these have demonstrated significant property differentials compared with malignant tumor properties, however each does have important limitations. For microbubbles, their relatively large size limits them to the vascular compartment, thereby reducing their potential effectiveness for targeting cancer cells. There is considerable potential for SWCNT because of their high dielectric properties; however, there are also very real questions about toxicity.